Adamantane derivatives 1-halo-derivative

It IS well known that adamantane or its 1-halo derivatives, for example 50, can be easily transformed into a stable tertiary 1-adamantyl cation 26. As was already mentioned vide supra), this cation owes its increased stability to the unique stabilization effects involving the participation of the remote centers in the charge delocalization. The pattern of NMR spectra may be used as a sensitive probe to the charge delocalization effects. Thus for the series of aliphatic tertiary carbenium ions, the presence of the positive charge induces a downfield shift of the H NMR signals (relative to those of the parent covalent precursor) at the adjacent centers. The magnitude of this effect decreases in the order S> y In the case of 26, a substantial downfield shift of -protons is also observed, but this effect is pronounced even stronger for the y-protons... 

The reactions of 1,3-dihaloadamantanes with various carbanions in DMSO have been studied.18 For example, potassium enolates of acetophenone and pinacolone and the anion of nitromethane react with 1,3-diiodoadamantane (19) under photo-stimulation a free-radical chain process forms a 1-iodo monosubstitution product (20) as an intermediate, which undergoes concerted fragmentation to yield derivatives of 7-methylidenebicyclo[3.3.1]nonene (21). These and other results were interpreted in terms of the Srn1 mechanism. The work has been extended to the reactions of 1- and 2-halo- and 1,2-dichloro-adamantanes, examples of the SrnI mechanism again being found.19... 

Protoadamantanone is a versatile intermediate for the synthesis of not only protoadamantane derivatives,but also 1,2- and 2,4-disubstituted adamantanes, 2-substituted noradamantanes, and 4(5)-substituted 4-homoprotoadamantanes. 4-Protoadamantanone has been prepared by the nitrous acid deamination of 2-amino-l-adamantanol (77%), by aprotic diazo-tization of endo-7-aminomethylbicyclo[3.3.1]nonan-3-one in benzene with an equivalent amount of acetic acid (67%), and by thermolysis of 1-adamantyl hypohalites followed by base-promoted cyclization of the resulting halo ketones (32-37%).In spite of low and erratic yields, the last reaction sequence has provided the most convenient route to the protoadamantanes, since the other two approaches require lengthy syntheses of the starting materials. 

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